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首页> 外文期刊>Journal of Nuclear Materials: Materials Aspects of Fission and Fusion >Cluster dynamics simulation of xenon diffusion during irradiation in UO2
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Cluster dynamics simulation of xenon diffusion during irradiation in UO2

机译：UO2辐照期间氙气扩散的集群动力学模拟

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Diffusion of fission gas in UO2 nuclear fuel impacts several important performance metrics, such as fission gas release, swelling, and thermal conductivity. Current empirical models of fission gas release have significant uncertainty, some of which derives from the bulk diffusion rate and its dependence on, for example, fuel chemistry and irradiation. We have applied the previously-developed Free Energy Cluster Dynamics (FECD) methodology in the code Centipede to calculate xenon cluster concentrations in UO2 under intrinsic (high temperature) and irradiation-enhanced (intermediate temperature) conditions in order to develop a model of the xenon diffusion coefficient based on the atomic scale mechanisms responsible for transport. While the diffusion mechanism for xenon in UO2 is adequately described by the Xe + U2O vacancy cluster for intrinsic conditions, a similar process is not capable of capturing measured in-pile fission gas diffusivity at intermediate temperatures. Therefore, a different diffusion mechanism must dominate under this regime. Using calculated atomistic data, we have shown that irradiation-enhanced diffusion at intermediate temperatures occurs via the larger Xe + U4Oy vacancy clusters, which have lower migration barriers and increase in concentration by several orders of magnitude compared to intrinsic conditions. This mechanism is enabled by the increased uranium vacancy concentration under irradiation due to Frenkel pair production. In addition, the fast migration of uranium interstitials with two attached oxygen interstitials lowers the total uranium interstitial concentration through reactions with sinks. This allows the extended defects, such as Xe + U4Oy vacancy clusters, to maintain high concentrations by limiting annihilation with attached vacancies. Predictions using the Xe + U4Oy diffusion mechanism are in good agreement with experiment, albeit with some differences in the Arrhenius slope, which we believe may be related to either experimental or model parameter uncertainty. Finally, an analytical expression suitable for application in fuel performance simulations was derived to capture the predictions of the Centipede simulations. Published by Elsevier B.V.
机译：在UO2核燃料影响到的几个重要的性能指标，如裂变气体释放，肿胀，热传导性裂变气体的扩散。裂变气体释放的电流的经验模型具有显著的不确定性，其中的一些从所述体积扩散率及其对依赖，例如，燃料的化学和照射导出。我们已经在代码施加的先前开发的自由能群集动力学（FECD）方法蜈蚣到计算氙簇浓度在UO 2下的本征（高温）和照射增强（中间温度）条件下，以开发氙的模型根据负责运输原子尺度机制扩散系数。而在UO2氙扩散机构被充分地用于固有条件的Xe + Li 2 O空位簇描述的，类似的处理不能够在中间温度上俘获测定桩裂变气体扩散性的。因此，不同的扩散机制必须在此制度下，占主导地位。使用计算出的原子论数据，我们已经表明，在中间温度照射增强扩散经由较大的Xe + U4Oy空位团，其具有由数个数量级相比固有的条件下迁移的障碍和增加浓度发生。这种机制是通过照射下增加的铀空位浓度因弗伦凯尔对生产允许。此外，铀插页的具有两个连接的氧插页快速迁移降低了通过与水槽反应总铀间质性浓度。这允许扩展的缺陷，例如氙+ U4Oy空位簇，通过限制湮灭附着空位以维持高浓度。使用氙气+ U4Oy扩散机制的预测是吻合良好的实验，尽管在阿累尼乌斯斜率一定的差异，我们认为可能与实验或模型参数的不确定性。最后，适合于在燃料性能仿真应用的解析表达式推导捕捉蜈蚣模拟的预测。由elsevier b.v出版。

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